IGES

IGES stands for Initial Graphics Exchange Specification and was written by a
panel for the National Bureau of Standards. The strongest argument for
IGES is its high level of support by CAD packages running on the
larger computer systems.
IGES is both a 2D and 3D format.

A simple example IGES file (so you may recognise one when you see it) is shown below.
Each line is based upon a 80 character string, from the era of 80 character
punch card readers from the computers of the 70's and 80's running early
versions of FORTRAN.
Data containing text strings are stored in so called "Hollerith"
format, that is a number which is the length of the string, followed by an "H",
followed by the string itself. For example the line after the header line below
is: ", ; box+line.IGS box+line.IGS CGT v1.0 IGES 3.0 16 8 24 8".

The character in column 73 determines the type of data on the line, this may be
S, G, D, P, or T standing for Start, Global, Directory Entry, Parameter Data, and Terminate.